This invention relates to key switching and more particularly to a resilient key switch actuator and assembly that provides a tactile feel to an operator.
Individual key switches and keyboards using them find wide use in such diverse product applications as data input terminals, typewriters, computer keyboards, cash registers, and calculators. Individual keys usually have alphanumeric characters or other symbols inscribed on them. When an operator depresses a key, its associated key switch closes a circuit. And the closed circuit provides an electric output that may be stored or that may cause performance of some operation, such as issuing a character.
It is highly desirable to provide key switches with a resilient actuator arrangement that provides a tactile feel to an operator during a key stroke. This tactile feel is established by a key switch using a resilient actuator that effects a steep drop-off in reactive or resistive force. This drop-off indicates to an operator that switch closing or triggering has been made.
At present there are three major approaches to resilient key switch actuator arrangements. The operation of these approaches is generally indicated in the three force displacement curves shown in FIGS. 1-3.
FIG. 1 shows a force displacement curve for a keyboard key switch using what is referred as a linear type actuator arrangement. As indicated in FIG. 1, reactive or resistive force increases at a particular slope from point "a" to point "b" as an operator depresses a key. At point "b" switch triggering begins. Thereafter, reactive force continues to increase with compression displacement from points "b" to "c", but at an increased slope. As the operator releases the key, restoring force of the actuator moves the actuator in expansion toward its initial position generally along the same curve, but in the opposite direction.
FIG. 2 shows a force displacement curve for a keyboard key switch using what is referred to as a tactile type actuator arrangement. As indicated in FIG. 2, reactive or restive force typically increases from point "a" to a maximum resistive force location at point "b" as an operator depresses a key. At location "b" reactive force drops-off quickly (tactile drop-off) with a small amount of displacement to provide the operator with a tactile feel. The tactile drop-off continues until switch triggering begins at point "c". Thereafter, reactive force continues to increase with compressive displacement from point "c" to point "d". As the operator begins to release the key, restoring force moves the arrangement in expansion toward its initial position generally along the same curve, but in the opposite direction.
FIG. 3 shows a force displacement curve for a keyboard key switch using what is referred to as a hysteresis type actuator arrangement, which represents the third major approach. As indicated in FIG. 3, reactive force increases in a substantially linear way from point "a" to a point of maximum reactive force at point "b" as an operator depresses a key. At point "b" reactive force plummets or vertically drops-off to point "c" with little, if any, further displacement. This precipitous tactile drop-off provides the operator with a pronounced tactile feel. And at point "c" switch triggering begins. Thereafter, reactive force increases as the operator continues compression displacement from point "c" to point "d". As the operator begins to release the key, initial expansion displacement takes place along the same curve, but in the opposite direction-that is total displacement moves from point "d" to point "c". But thereafter the return or expansion displacement path is different from the initial or compression displacement path. As indicated by the dashed lines, the return path moves past point "c" to a smaller total displacement at point "e". At point "e" there is an abrupt vertical increase in restoring force with little, if any, change in displacement. This abrupt increase is shown in dashed lines from point "e" to point "f". This places the restoring force at point "f", which is located at a lower force level on the initial path than the level of reactive force at tactile drop-off (point "b").
The phenomenon known as hysteresis, which operates along a return path different from an initial path, is the basis for a key switch closure that reduces the problem of bouncing. As shown in FIG. 3, reduced bouncing is accomplished by tactile drop-off occurring during compression displacement from point "b" to point "c", which initiates switch closure, and by abrupt increase occurring during expansion displacement from point "e" to point "f" by restoring force, which initiates switch opening.
While there has been a variety of approaches employed to improve each of the three types actuator arrangements discussed, they all still tend to have deficiencies in one aspect or an other, including such things as: mechanical breakdown of parts (such as springs), high cost of manufacture (both piece cost and assembly cost), and undesirable chattering or bouncing requiring additional "de-bouncing" techniques. Consequently, there has been a variety of efforts in the art to overcome these deficiencies. But the need continues.
Experience has shown that in most instances key switches using a hysteresis type actuator provides significant advantages over actuator arrangements using the other two approaches, particularly in tactile feel and "de-bouncing". But prior art hysteresis arrangements use both springs and cups and are plagued by the same types of deficiencies as other resilient key switch response arrangements. Consequently, hysteresis type actuators have problems and are expensive to manufacture. They can involve over two hundred parts per keyboard. And these many parts can contribute to breakdowns over the life of the product.
Accordingly, there is a need for a simple and more effective hysteresis type key switch actuator arrangement.